How Does a Fanless PC Work?

A fanless PC works by moving heat from the processor, memory, storage and power circuitry into its metal chassis through heatsinks, thermal pads and heat pipes, then letting the finned outer case pass that heat to the surrounding air by natural convection and radiation. There is no fan, so no air is drawn through the computer and nothing in the cooling path moves.

If you are familiar with how a typical fanned computer stays cool, you are already halfway there. A desktop PC blows air across its heatsinks; a fanless PC reaches the same goal passively, through natural convection or conduction. Because it needs no airflow inside, the chassis can be built without vents, which matters in the many industrial settings where the air carries dust, fibers, oil mist or moisture that would otherwise settle on circuit boards. A sealed case keeps those contaminants out and removes the fan, the part most likely to wear out.

This guide follows the heat from the silicon to the air: the materials in the heat path, how heat pipes and fins work, the difference between convection and conduction cooling, how much processor power a fanless chassis can handle, what happens as the ambient temperature rises, and the installation rules that keep the system cool once it is in place.

Every watt the processor uses ends up as heat, and that heat has to cross a chain of materials before it reaches the air. Each link in the chain resists the flow a little, and the temperature of the silicon is set by the total resistance of the chain plus the temperature of the air at the end of it. A good fanless design keeps every link short, wide and well bonded.

Other hot parts follow the same route. Memory, NVMe SSDs, network controllers and the voltage regulators that power the processor all sit against pads that bond them to the chassis or to a secondary heat spreader, so no component relies on air moving inside the case. That matters because the inside of a sealed fanless computer has almost no airflow: anything not bonded to the metal simply warms the trapped air around it.

A worked example shows how far design can push this. The SolidRun Bedrock R8000 uses a double-layer heatsink with a chimney effect, double-sided copper heat pipes and a liquid metal thermal interface on its 45 W AMD Ryzen processor, with DDR5 memory, NVMe SSD and network controllers also bonded to the heat path to prevent hot spots. SolidRun quotes a 1.7× improvement in convection cooling from the design, covered in our note on its dual-layer heatsink.

Copper conducts heat well, but a solid copper bar long enough to reach a chassis wall would be heavy and still lose temperature along its length. Heat pipes solve that. Each is a sealed copper tube with a wick lining and a small amount of working fluid, usually water, under low pressure. At the hot end the fluid evaporates and absorbs heat; the vapor travels to the cool end, condenses on the chassis side and releases the heat; the wick then draws the liquid back. Because the heat rides on the vapor, a heat pipe moves far more heat than solid copper of the same size, with only a few degrees of difference between its ends.

A vapor chamber is the same idea in a flat plate, spreading heat in two directions rather than along a line. Under the pipes and chambers sits a heat sink or copper block bolted to the board, so the assembly stays in place under shock and vibration. The thermal interface material between the processor and the block matters more than its thin layer suggests, because air is a very poor conductor and even a small gap adds resistance.

The figures vary with grade and supplier, so treat them as orders of magnitude. The lesson is in the bottom row: the heat path works only when every gap is filled with something far better than air, which is why the mounting pressure and the interface material are part of the thermal design, not an assembly detail.

Once the heat reaches the outer case, two mechanisms remove it. Natural convection is the main one: air touching the warm fins heats up, becomes less dense and rises, drawing cooler air in behind it. No fan is needed, but the flow is gentle, so the fins have to be designed for it. Radiation does the rest, as the warm surface emits infrared energy to cooler surroundings. In still air radiation can carry a meaningful share of the heat, often quoted at around a quarter or more for a dark, anodised case, which is one reason many fanless chassis are black.

Fin design is a balance. More fins add surface area, but fins packed too closely trap a layer of slow-moving air between them and cool less well in natural convection than fewer, wider-spaced fins. Tall vertical fins work like a chimney, accelerating the rising air, which is why most finned fanless PCs are designed to be mounted with the fins running vertically.

Because the fins rely on the air around them, the rating of a finned fanless PC always assumes open space. Mount it in a closed box, lay it flat with the fins facing down or let cables cover the top, and the same chassis will run hotter. Our guide to thermal throttling explains what the processor does when that heat has nowhere to go.

In a sealed cabinet the air inside warms up and stays warm, so fins have little to work with. Conduction cooling takes a different route. The computer has a flat heatsink face, the heat path inside runs to that face, and the system is bolted to a metal cabinet wall, a cold plate or a vehicle structure that conducts the heat away to the outside.

The Neousys Nuvo-9531-FT is an example. Its flattop heatsink sits against the cabinet wall, its 65 W desktop processors are configured to a 35 W TDP for the fanless envelope, and Neousys rates it from −25 to 60 °C when mounted on an aluminum panel that simulates a cabinet wall. The rating depends on that mounting: the wall is part of the cooling system, so a thin plastic panel or a painted, uneven surface will not do the same job. Some designs, such as the SolidRun Bedrock Tile enclosure, offer the same choice in one range, with a slim build cooled into a cold plate or chassis wall.

Our guide to edge computers for confined, sealed and waterproof enclosures covers conduction-cooled systems in more depth.

A fanless chassis is designed to remove a maximum sustained processor power at a maximum ambient temperature. The processor figure is its TDP, the sustained heat the cooling must remove, explained in our guide to processor TDP and base power. Short turbo bursts above the TDP are absorbed for a while by the thermal mass of the metal, but once the chassis has warmed through, the sustained power settles at what the fins or the mounting face can shed.

Manufacturer ratings show the trade-off. The Vecow ECX-3000 is rated for fanless operation from −40 to 75 °C with 35 W processors and from −40 to 55 °C with 65 W parts: the same chassis gives up 20 °C at the top of its range for the extra 30 W. At the low-power end, the Vecow SPC-9000 family shows the effect of fin area. The SPC-9100-165U carries a full finned heatsink on its 15 W class Intel Core Ultra 7 165U and is rated from −40 to 75 °C with airflow, while the slimmer heat-spreader build in the same series suits cooler locations.

The lowest class is where most industrial mini PCs sit, because a small case has little fin area. The figures that matter are the ones in the footnotes: which processor, at which ambient, in which orientation, with how much airflow. Two fanless PCs with the same processor can have quite different ratings because their chassis differ.

A fanless PC cannot cool its processor below the air around it. The chassis surface runs some degrees above ambient to push heat into the air, the internal path adds more, and the silicon sits at the top of that stack. Raise the ambient by 10 °C and, to a first approximation, everything inside rises by 10 °C too. That is why a fanless rating is always a pair of numbers: a processor power and a maximum ambient.

An illustrative example: a chassis that rises about 1 °C above ambient for every watt it sheds will sit around 35 °C above the air at a 35 W sustained load. In a 25 °C room the case surface is around 60 °C, warm to the touch but well within design. In a 55 °C cabinet the same load puts the case near 90 °C and leaves little margin for the processor, which then holds its temperature by lowering its clock speed.

The table is a general guide, not a rating for any one product; always work from the manufacturer’s figures for the exact processor. Storage and memory need the same margin: wide-temperature systems usually require industrial SSDs and memory to reach the top and bottom of their ranges. Our wide temperature computers are rated for installations that see heat or deep cold, and the industrial temperature range explainer sets out what the common ratings mean.

Passive cooling is one of three ways to keep a computer within its limits. The table summarizes the trade-offs; our comparison of active vs passive cooling covers them in detail, including hybrid designs that keep the processor fanless and give a GPU its own airflow.

Removing the fan also helps reliability on paper as well as in practice, because a fan is one of the few wear parts in a computer and adds its own failure rate. Our guide to MTBF shows how much difference that can make to a predicted figure, and solid-state industrial PCs covers the wider idea of a computer with no moving parts at all.

These four systems from our range show the methods described above in real chassis. We configure the BIOS power limits to suit the enclosure, fit industrial memory and storage, image the operating system and test each computer before it ships. Our guide to the benefits of fanless computers covers why passive cooling suits industrial sites, and fanless industrial mini PCs covers the smallest designs.

For Jetson-based systems the same principles apply to a module rather than a socketed processor, and our Jetson thermal design guide covers power modes and heatsink choices for them.